1. Field of the Invention
This invention relates to compositions and procedures for the treatment of wood and wood products, for protection during storage and handling of the lumber, or as a primer of sheathing. It also relates to the treated wood product so formed.
2. Description of the Prior Art
A piece of timber, due to the manner of its formation, possesses anisotropic structure which influences its properties and behaviour. Compared to competitive cladding materials, for example metals and plastics materials, it has a number of major disadvantages which tend to counteract the advantages of strength, lightness, low thermal expansion and desirable aesthetic features. To overcome and minimize these disadvantages a number of specific problems exist: the wood must be protected against degrading environmental factors (namely, moisture cycling, photodegradation and biological attack); the dimensional stability with respect to moisture cycling must be improved; photodegradation due to sunlight must be minimized; the resistance to biological attack (fungus) must be improved; the adhesion of protective and decorative coatings must be improved; and extractives which adversely affect protective and decorative properties of coatings must be sealed within the wood. All these aims should be achieved with a treatment that does not alter the natural beauty of wood.
Four classes of treatments are currently used in an attempt to meet these requirements.
The first class is that of clear or pigmented penetrating systems which contain fungicides and water-repellent additives, such as, for example, polyethylene waxes and metal stearates in a non-aqueous solvent media. These treatments are deficient in that they must be repeated at regular intervals of 1 to 2 years to provide a desired level of protection.
The second class is that of stains and sealers. These are normally synthetic resin solutions, usually pigmented and designed to penetrate the surface of the wood. These treatments as well as deficient, and should be repeated every 1 or 2 years in order to provide the required degree of protection.
The third class is that of paint systems. Such paint systems would normally consist of a primer and top coats. When well applied, these will provide the exterior cladding protection from 2 to 5 years.
The fourth class is that of salt treatments. A number of salt treatments have been suggested, the most common of which are known as copper-chrome arsenate (CCA) and acid-copper-chromate (ACC). Presently systems of this type are effective to provide relatively long term durability when applied by pressure impregnation techniques. The CCA systems are believed to become fixed in the wood by oxidation-reduction reactions associated with the chromic acid in the compositions and it is these same reactions which are believed adversely to affect stability and processing characteristics. Moreover, while providing a high level of protection against fungal attack, they provide only limited protection against weathering.
Copper and zinc containing fungicides have been proposed (see U.S. Pat. No. 2,414,661 issued Jan. 21, 1947 to A. A. Nikitin) which were prepared by precipitation from an aqueous solution of a zinc salt and a copper salt with an alkali solution containing soya bean protein, or soaps of fatty acids.
Fungicides have been proposed for cellulosic materials (see U.S. Pat. No. 2,423,619 issued July 8, 1947 to L. Roon) which comprise copper soaps formed in situ from an aqueous solution of copper salts and aqueous ammonia by reaction with fatty acids.
It has also been proposed to provide water and fire resistant coatings on wood (see U.S. Pat. No. 2,530,458 issued Nov. 21, 1950 to H. R. Frisch) by the use of zinc orthophosphate or zinc orthoarsenate compositions applied as a concentrated solution in aqueous ammonia. Zinc arsenate, zinc arsenite, and zinc phosphate can all be applied from ammonia solution and, on drying, the salt is insoluble and fixed in the wood. However, in all of these cases the weather resistance of the treated wood is not significantly improved.
It was proposed to improve the hardness, compressive strength hygroscopicity and liability to swell of wood by impregnating the wood with an aqueous ammoniacal solution of polycarboxylic acid containing at least 6 carbon atoms. (See U.S. Pat. No. 2,768,910 issued Oct. 30, 1956 to H. Krzikalla and O. Lissner).
U.S. Pat. No. 2,772,263 issued Nov. 27, 1956 to C. C. Yeager proposed to use a compound having a high fungicidal activity in wood, which is a metal rosin ammonium phenoxide, prepared by reacting a rosin ammonium phenoxide with a water soluble salt of a metal capable of forming a complex with ammonia.
U.S. Pat. No. 3,007,844 issued Nov. 7, 1961 to W. O. Schuly proposed the use of a composition comprising a heavy metal ion, borate ions and chromate ions as an impregnating agent for the preservation of wood.
U.S. Pat. No. 3,105,773 issued Oct. 1, 1963 to S. Frank and D. C. Wehner proposed to preserve wood by imparting pesticidal and anti-thallophytic properties by first impregnating the wood with a water soluble heavy metal salt, and then with an acrylic polymer solution.
Canadian Pat. No. 568,393 of Hager discloses as a wood treating composition an aqueous ammoniacal solution of copper and zinc salts with carbonate ions, and optionally also containing pentachlorophenol and/or arsenic salts.
Ammoniacal copper arsenite compositions are presently being used as presevatives.